LONG-TERM STABILITY OF ORGANIC SELENIUM SPECIES IN AQUEOUS-SOLUTIONS

Long term stability of organic selenium compounds (selenocystine, sele nomethionine, trimethylselenonium ion) has been studied over a one yea r period for 2 analyte concentrations: 25 and 150 mu g/L Se. at pH 4.5 in the dark, under different storage conditions: temperature of -20 d egrees C, 4 degrees C, 20 degrees C, 40 degrees C; in Pyrex, Teflon, o r polyethylene containers; in an aqueous matrix or in the presence of a chromatographic counter ion (pentyl sulfonate at 10(-4) mol/L concen tration). Light effects have also been tested. The stability of the se lenium species was monitored by HPLC-ICP/MS. Storage conditions can dr astically alter the stability of organic selenium species. Organoselen ium compounds were shown to be stable in the dark over a one year peri od in an aqueous matrix at pH 4.5 in Pyrex containers at both 4 degree s C and 20 degrees C. Pyrex vials exposed to natural sunlight at room temperature resulted in a steady decrease of the selenoamino acid conc entration. Teflon containers caused losses of less than 25% at both 4 degrees C and 20 degrees C in the dark. However, polyethylene vials pr esented, at all tempera tures tested, a rapid decrease of the TMSe+ co ncentration. The stability of the Se species studied did not show sign ificant differences between 4 degrees C and 20 degrees C in any contai ner material used. Storage of solutions at 40 degrees C led to slight differences between the Pyrex and Teflon containers. However, polyethy lene presented a drastic decrease of the three species over time at th is higher temperature, Solutions frozen at -20 degrees C in polyethyle ne vials did not stabilize the TMSe+ signal. Finally, concentrations a nd matrices of the samples did not significantly affect the stability of the species.